230 Dr. C. F. J. Lachmann on the Organization of Infusoria. 



modes of reproduction of the Infusoria. In them we meet with 

 an undoubtedly asexual reproduction, and also with a mode of 

 propagation which it is probable will hereafter be proved to be 

 of a sexual nature, or which must be regarded as the analogue 

 of the sexual repi'oduction of the higher animals, — namely, a 

 propagation by embryos. The purely vegetative mode of pro- 

 pagation consists in fissation and gemmation. 



Fissation, as is well known, is the most widely-diffused mode 

 of propagation of the Infusoria, and the one with which we have 

 been longest acquainted. Nevertheless, it has not been so 

 closely studied as, perhaps, it deserved ; for our knowledge of it 

 has made but little progress since Trembley's beautiful descrip- 

 tion of the fissation of the Stentors. By the generalization of a 

 few observations, principally with reference to the cell-theory, 

 we have come very recently to believe that the nucleus always 

 induces the fissation by its becoming divided, or at least con- 

 stricted. This view, however, is not correct. There are cer- 

 tainly cases in which the nucleus first of all divides, but in other 

 cases its division only takes place when the rest of the body is 

 already far advanced in division ; and in others again the actual 

 fissation of the nucleus does not lead to that of the body, but 

 embryos are developed in it, as we shall soon show. The fissa- 

 tion is generally commenced rather by a new formation of con- 

 tractile vesicles*, from dilatations of the existing vessels, as 

 appears from Stein's observations on Stentor. In those Infusoria 

 in which a peculiar series of stronger cilia leads to the mouth 

 (such as OxytrichincE and Euplotecp), the furrow in which this 

 series of cilia is situated, is seen subsequently [to,] or simulta- 

 neously [with the division of the contractile vesicle] to become 

 produced backwards over the mouth ; in this prolongation cilia 

 are produced, and its posterior extremity becomes deepened into 

 a mouth and cesophagvis, which then opens towards the alimen- 

 tary cavity of the animal ; then, simultaneously with the external 

 constriction of the body, the new furrow is separated from the 

 old one. (In Stentor the new frontal series of cilia first makes 

 its appearance on the old animal as a lateral, straight series, — 

 the crista lateralis of Ehrenberg.) In animals which also possess 

 peculiar processes of the body as organs of motion (hooks, 

 styles, &c.), the fissation usually takes place in such a manner, 

 that each of the newly-formed animals acquires a portion of 

 these from the old animal, whilst the other part is of new form- 



* Even Ehrenberg refers to this in some cases. Wiegmann adduces it 

 in sup])ort of his opinion that the contractile vesicle is to be regarded as 

 the heart. The greater part of the following observations on the develop- 

 ment of the Infusoria were made by me in conjunction with my friend, E. 

 Claparede. 



